Editing IPCC:AR6/Data/Glossary (section)

== U ==

<div class="glossary-entry">
<div id="Uncertainty"></div>
=== <span class="glossary-term">Uncertainty</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGII; WGIII</div>

<div class="glossary-definition">'''Definition:''' A state of incomplete knowledge that can result from a lack of information or from disagreement about what is known or even knowable. It may have many types of sources, from imprecision in the data to ambiguously defined concepts or terminology, incomplete understanding of critical processes or uncertain projections of human behaviour. Uncertainty can therefore be represented by quantitative measures (e.g., a probability density function) or by qualitative statements (e.g., reflecting the judgement of a team of experts) (Moss and Schneider, 2000; IPCC, 2004; Mastrandrea et al., 2010).</div>
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<div id="United_Nations_Convention_to_Combat_Desertification"></div>
=== <span class="glossary-term">United Nations Convention to Combat Desertification</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGIII</div>

<div class="glossary-longer-term">'''Full term:''' United Nations Convention to Combat Desertification (UNCCD)</div>

<div class="glossary-definition">'''Definition:''' A legally binding international agreement linking environment and development to sustainable land management, established in 1994. The Convention’s objective is ‘to combat desertification and mitigate the effects of drought in countries experiencing drought and/or desertification’. The Convention specifically addresses the arid, semi-arid and dry sub-humid areas, known as the drylands, and has a particular focus on Africa. As of September 2020, the UNCCD had 197 Parties.</div>
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<div id="United_Nations_Framework_Convention_on_Climate_Change"></div>
=== <span class="glossary-term">United Nations Framework Convention on Climate Change</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGII; WGIII</div>

<div class="glossary-longer-term">'''Full term:''' United Nations Framework Convention on Climate Change (UNFCCC)</div>

<div class="glossary-definition">'''Definition:''' The UNFCCC was adopted in May 1992 and opened for signature at the 1992 Earth Summit in Rio de Janeiro. It entered into force in March 1994 and, as of September 2020, had 197 Parties (196 States and the European Union). The Convention’s ultimate objective is the ‘stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system’ (UNFCCC, 1992). The provisions of the Convention are pursued and implemented by two further treaties: the Kyoto Protocol and the Paris Agreement.</div>
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<div class="glossary-entry">
<div id="Uptake"></div>
=== <span class="glossary-term">Uptake</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGII; WGIII</div>

<div class="glossary-definition">'''Definition:''' The transfer of substances (such as carbon) or energy (e.g., heat) from one compartment of a system to another; for example, in the Earth system from the atmosphere to the ocean or to the land.</div>
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<div class="glossary-entry">
<div id="Upwelling_region"></div>
=== <span class="glossary-term">Upwelling region</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGII</div>

<div class="glossary-definition">'''Definition:''' A region of an ocean where cold, typically nutrient-rich waters well up from the deep ocean.</div>
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<div class="glossary-entry">
<div id="Urban_Systems"></div>
=== <span class="glossary-term">Urban Systems</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGII; WGIII</div>

<div class="glossary-definition">'''Definition:''' Urban systems refer to two interconnected systems-first, the comprehensive collections of city elements with multiple dimensions and characteristics: a) encompass physical, built, socioeconomic-technical, political, and ecological subsystems; b) integrate social agent/constituency/processes with physical structure and processes; and c) exist within broader spatial and temporal scales and governance and institutional contexts; and second, the global system of cities and towns.</div>
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<div id="Urban"></div>
=== <span class="glossary-term">Urban</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGII; WGIII</div>

<div class="glossary-definition">'''Definition:''' The categorisation of areas as 'urban' by government statistical departments is generally based either on population size, population density, economic base, provision of services, or some combination of the above. Urban systems are networks and nodes of intensive interaction and exchange including capital, culture, and material objects. Urban areas exist on a continuum with rural areas and tend to exhibit higher levels of complexity, higher populations and population density, intensity of capital investment, and a preponderance of secondary (processing) and tertiary (service) sector industries. The extent and intensity of these features varies significantly within and between urban areas. Urban places and systems are open with much movement and exchange between more rural areas as well as other urban regions. Urban areas can be globally interconnected facilitating rapid flows between them – of capital investment, of ideas and culture, human migration, and disease.</div>
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<div id="Urban_and_peri-urban_agriculture"></div>
=== <span class="glossary-term">Urban and peri-urban agriculture</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGII</div>

<div class="glossary-definition">'''Definition:''' The cultivation of crops and rearing of animals for food and other uses within and surrounding the boundaries of cities, including fisheries and forestry (EPRS, 2014).</div>
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<div class="glossary-entry">
<div id="Urban_heat_island"></div>
=== <span class="glossary-term">Urban heat island</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI; WGIII</div>

<div class="glossary-longer-term">'''Full term:''' Urban heat island (UHI)</div>

<div class="glossary-definition">'''Definition:''' The relative warmth of a city compared with surrounding rural areas, associated with heat trapping due to land use, the configuration and design of the built environment, including street layout and building size, the heat-absorbing properties of urban building materials, reduced ventilation, reduced greenery and water features, and domestic and industrial heat emissions generated directly from human activities.</div>
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<div class="glossary-entry">
<div id="Urbanisation"></div>
=== <span class="glossary-term">Urbanisation</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGII; WGIII</div>

<div class="glossary-definition">'''Definition:''' Urbanisation is a multi-dimensional process that involves at least three simultaneous changes: (i) land use change: transformation of formerly rural settlements or natural land into urban settlements; (ii) demographic change: a shift in the spatial distribution of a population from rural to urban areas; and (iii) infrastructure change: an increase in provision of infrastructure services including electricity, sanitation, etc. Urbanisation often includes changes in lifestyle, culture, and behaviour, and thus alters the demographic, economic, and social structure of both urban and rural areas. (Stokes and Seto 2019; Seto et al. 2014; UNDESA 2018)</div>
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<div class="glossary-entry">
<div id="Urbanization"></div>
=== <span class="glossary-term">Urbanization</span> ===

<div class="glossary-working-groups">'''Working Groups:''' WGI</div>

<div class="glossary-definition">'''Definition:''' In the WGI report, urbanization is used to mean the process of soil sealing with the change of natural land cover to built environment and urban areas, together with its associated albedo changes, and increased surface runoff and elevated warming.</div>
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<div class="glossary-letter-section">